Sandbox c1

 1ACJ shows the crystal structure of Torpedo californica acetylcholinesterase (TcAChE) complexed with tacrine.

Tacrine is a parasympathomimetic and a centrally acting cholinesterase inhibitor.

It was the first centrally-acting cholinesterase inhibitor approved for the treatment of Alzheimer's disease.

Tacrine’s ring is stacked between the aromatic rings of tryptophan 84 and phenylalanine 330 (W84 and F330).

(W84 and F330)

Harel M, Schalk I, Ehret-Sabatier L, Bouet F, Goeldner M, Hirth C, Axelsen PH, Silman I, Sussman JL. Quaternary ligand binding to aromatic residues. in the active-site gorge of acetylcholinesterase. Proc Natl Acad Sci U S A. 1993 Oct 1;90(19):9031-5. PMID:8415649.

How do we get the oxygen we breathe?
Oxygen is required by all aerobic animals as a basic mechanism to accept electrons and hydrogen ions produced during metabolism. Even when oxygen is all around us, in the air and in the water, oxygen need to be close to the cells where it's going to be used.